1. Field of the Invention
The present invention relates to centrifuges and, more particularly, to the means for fastening the sensor for registering the rotation speed of the centrifuge rotor and can be utilized mostly for controlling the rotation speed of the centrifuge rotor that might be required in biotechnology, biophysics, biology and other fields.
2. Description of the Related Art
It is commonly known that the rotation speed of the centrifuge rotor shall not exceed a preset value since it may result in serious troubles including breakage of the rotor and a complete failure of the centrifuge.
It becomes particularly important because the rotors of modern centrifuges revolve at speeds reaching scores of thousands of rpm. Therefore, each design of the centrifuge incorporates a sensor whose function is to check the rotation speed and to cut off the power supply and, consequently, stop the rotor if its speed rises above the preset value.
As a rule, this problem is solved by the provision of a disc secured on the lower face of the rotor and having alternating marks differing, for example, in their colour. These marks are read off by an oppositely-installed sensor, for example an optical one.
Whatever the type of the sensor, it must have an optimum sensitivity to the rotation speed of the rotor which can be attained by changing the sensor's position. The design of the device for installing the sensor and adjusting its position shall be compact because the space for accommodating said sensor in any type of centrifuge is always limited by the distance between the drive and the rotor.
Besides, the design should be highly reliable both from the standpoint of fixing the sensor in the position selected by adjustments and from the standpoint of installing and removing it, for example during preventive maintenance.
Known in the prior art is a device (U.S. Pat. No. 3,693,023) which can serve for controlling the rotation speed of the centrifuge rotor. However, the design of this device prevents adjusting the position of the sensor with regard to its optimum sensitivity to the rotation speed of the rotor.
Besides, this design comprises a great number of elements and is, therefore, quite complicated. The use of this design proves to be impracticable in view of its complexity and insufficient reliability caused by the impossibility of optimization of the sensor sensitivity to the rotation speed of the rotor.
Also known in the art is a centrifuge (EP, A, No. 0139290) wherein there is a provision for changing the position of the sensor with respect to its optimum sensitivity to rotation speed of the centrifuge rotor. The sensor is located on a mounting plate accommodated in a recess of the ring installed on the mounting surface of the casing of the drive which revolves the centrifuge rotor.
The centrifuge comprises a rotor-revolving drive and the rotor speed is controlled by a sensor (photosensor) located on a mounting plate accommodated in a recess of the supporting ring installed on the mounting surface of the drive casing. The sensor is capable of moving relative to the lower surface of the rotor, to the position of maximum sensitivity to its rotation speed. Installed on the lower surface of the rotor is a special speed indicator. A photosensitive device registering the rotation speed of the rotor is installed on the mounting plate of the sensor, said plate being provided with a projection of a sufficient size for installing the photosensitive device on the mounting plate. The mounting plate of the photosensor is linked with the supporting ring by two adjusting elements located on the ends of the mounting plate. These adjusting elements displace the mounting plate complete with the photosensor relative to the supporting ring thus setting the photosensitive device at an optimum distance from the speed indicator located on the lower surface of the rotor.
However, the design of this device is complicated and comprises a large number of fasteners of both the ring and mounting plate. The main ring fastening element has various complicated cutouts and junctions. In view of the fact that the position of the sensor is adjusted by shifting the mounting plate with the aid of two adjusting elements (screws), even concurrent rotation of said screws fails to ensure strict vertical orienting of the sensor relative to the lower surface of the centrifuge rotor. This inevitably reduces the accuracy of measuring the rotor speed and, as a consequence, affects the reliability of the centrifuge. In addition, the very process of adjustment is highly labour-consuming and takes much time.
Another disadvantage of this centrifuge consists in that the photocell of the sensor is glued to the mounting plate. On the one hand, this denies the possibility of prompt replacement of the faulty photocell and, on the other, it reduces the reliability of the device. Thus, the known design is quite sophisticated, it hinders the process of adjustment and fails to ensure the requisite accuracy and reliability.